Prion diseases are fatal neurodegenerative illnesses that occur in genetic, sporadic and infectious forms (Glatzel, et al. (2005) Arch. Neurol. 62:545-552). From a public health perspective, prion diseases are challenging to control because infectious prions are highly resistant to environmental degradation (Brown & Gajdusek (1991) Lancet 337:269-270) and can potentially be transmitted by several different routes (Holada, et al. (2000) Lancet 356:1772; Ligios, et al. (2005) Nat. Med. 11:1137-1138; Mathiason, et al. (2006) Science 314:133-136; Seeger, et al. (2005) Science 310:324-326). The critical molecular event in the pathogenesis of prion diseases is the misfolding of the host-encoded prion protein (PrPC) into an infectious isoform (PrPSc), but the mechanism of this conformational change remains unknown (Prusiner (1982) Science 216:136-144). Mature PrP molecules contain 208 amino acid residues, two N-linked glycosylation sites, an intramolecular disulfide bond and a C-terminal glycophosphatidylinositol anchor (Endo, et al. (1989) Biochemistry 28:8380-8388; Locht, et al. (1986) Proc. Natl. Acad. Sci. USA 83:6372-6376; Stahl, et al. (1987) Cell 51:229-240; Turk, et al. (1988) Eur. J. Biochem. 176:21-30). Purified native PrPC molecules containing only prion protein and co-purified lipids have been converted into infectious PrPSc molecules de novo, through an in vitro reaction requiring accessory polyanions (Deleault, et al. (2007) Proc. Natl. Acad. Sci. USA 104:9741-9746).
Mammalian prions occur in a variety of different “strains”. Strains are defined as natural isolates of infectious prions characterized by distinctive clinical and neuropathological features, which are faithfully recapitulated upon serial passage within the same animal species (Bruce (1993) Br. Med. Bull. 49:822-838; Carlson (1996) Curr. Top. Microbial. Immunol. 207:35-47). Strain diversity is associated with variations in PrPSc conformation (Bessen & Marsh (1992) J. Viral. 66:2096-2101; Collinge, et al. (1996) Nature 383:685-690; Peretz, et al. (2001) Protein Sci. 10:854-863; Safar, et al. (1998) Nat. Med. 4:1157-1165; Telling, et al. (1996) Science 274:2079-2082), but it remains unknown precisely which PrPSc conformers or domains are required to encode mammalian prion strain phenotypes.
Various methodologies have been developed to analyze and detect the various forms of PrP. For example, conformation-dependent immunoassays (CDI) have shown that prion-infected brains contain both protease-sensitive and protease-resistant PrPSc molecules (Safar, et al. (1998) supra). In addition, chemical cross-linking of recombinant PrP to nanoparticles has been suggested for use in in vivo and in vitro manipulation of prion proteins to facilitate structural analysis (Kouassi & Irudayaraj (2006) J. Nanobiotech. 4:8).